1. Field of the Invention
The present invention relates to a structure of a transistor operable at a high frequency with high power.
2. Description of the Prior Art
In recent years, high speed IC's operable at a higher frequency than Si-IC's have been widely studied, which employ FET's using compound semiconductors such as GaAs-schottky gate FET's and AlGaAs/GaAs modulation doped FET. Such FET's, however, have poor capability of driving a large current and therefore do not exhibit the expected high operation speed in a case where they are combined in LSI.
Another attempt at a high speed IC has been carried out with use of hetero-bipolar transistors (HBT's) using, as a base region, a semiconductor having larger band gap than a semiconductor used for an emitter region. A typical example is an HBT using GaAs for the base region and AlGaAs for the emitter region, as reported in 1981 International Electron Devices Meeting Digest, pp. 629 to 632. These HBT's still involve a lot of problems. For examples, they have a complex structure and complicated manufacturing process, which make it difficult to use them in a high integration IC. Moreover, the capacitance between collector and base regions is too large to limit the high operability of the HBT's.